Running Poorly

[1984Silverado4x4]

I finally got tired of my 305 running on 5 or 6 cylinders so i got new plugs and wires for it. Now it pops and backfires and misses and lurches and chokes. It does alright in Low gear but its the worst when im in first gear until i give it some gas. then when i shift to second it chokes then takes of and accelerates fine until i get to third gear and it starts to diesel. it backfires and misses while im maintaining speed on a flat road but it idles fine. So whats wrong

[sick69]

Kinda sounds like you swapped a couple of wires to me. As in put them in the wrong place. Check numbers 5 and 7 those are an easy mistake.

Frank

[1984Silverado4x4]

Originally Posted by sick69

Kinda sounds like you swapped a couple of wires to me. As in put them in the wrong place. Check numbers 5 and 7 those are an easy mistake.

Frank

All of the wires are connected to the correct plug and terminal on the distributor

[1984Silverado4x4]

come on, i know theres gotta be some expert that can help me out here

[PhilaTruck]

I'm no expert, by any means. But have you considered the accelerator pump? How about the fuel filter? A little more information about the condition of the rest of the engine would help.

[1984Silverado4x4]

Originally Posted by PhilaTruck

A little more information about the condition of the rest of the engine would help.

Its a stock 305 never been rebuilt and has 97K miles on it.

And i asked a guy where i work about this and hes says it wouldnt be the timing, it might be the valves. And he told me to stick a vacuum gauge on it and it should read 14lbs at idle

[Ivan D.]

Originally Posted by 1984Silverado4x4

And i asked a guy where i work about this and hes says it wouldnt be the timing, it might be the valves. And he told me to stick a vacuum gauge on it and it should read 14lbs at idle

14lbs or 14"Hg? 14lbs of pressure/vacuum equals to about 28" Hg, which is way too much, actually dunno if it's even possible at all, unless during decel in gear with the foot off the throttle. 14" Hg sounds more like it, but it is kinda low, the 302 in my Lincoln with more than 155k on it still pulls over 22" Hg at 800rpm idle - me thinks unless something is messed up with yer engine or you got a big cam in it there should be more vacuum than 14" Hg, since it only gots less than 100k miles on it. If we're to keep it GM just for the sake of engine similarities my 350 pulls steady 16" at idle at 800rpms, cruising at like 18-1900 rpms gives me 13-14" Hg vacuum - I have a vacuum gauge in the truck, I drive by its readings and not by vehicle speed

[gchemist]

Check the timing, cap, bad wires, spark arching and advance.

[1984Silverado4x4]

Originally Posted by gchemist

spark arching and advance.

sorry i dont know what those are or how to check them

[knightlife]

might wanna check the distributor bro...its a common problem, a few degrees off can make that difference....loosen it up at the bolt a smidge to where you can free hand turn it..

from there turn it till it idles smoothly, then have someone turn off the truck ignition, and tighten the bolt down exactly on the perfect spot.

if that doesnt work, then unfortunately there are wires swapped or rubbing

[1984Silverado4x4]

Originally Posted by knightlife

might wanna check the distributor bro...its a common problem, a few degrees off can make that difference....loosen it up at the bolt a smidge to where you can free hand turn it..

from there turn it till it idles smoothly, then have someone turn off the truck ignition, and tighten the bolt down exactly on the perfect spot.

if that doesnt work, then unfortunately there are wires swapped or rubbing

played with the distributor and it runs good at idle. the wires are all in there correct spots and there not rubbing

[randyjohn]

funny, i got the same problem on my 350. idles fine then once you shift into drive it stalls and sputters. i just got the thing and haven't done anything to it yet. don't know when the last time the oil was changed or the tranny was flushed. first place i'm going is to change that oil. that sludge will do that to it once you put the motor under a load. then it's to the ignition.

[Yankeelights]

Sounds like a bad or stuck intake valve. If a lifter mushrooms at the bottom too much it can get stuck in its cylinder and hold the valve open and pop through the carb. Same pop if the valve goes bad.

[1984Silverado4x4]

Originally Posted by Yankeelights

Sounds like a bad or stuck intake valve. If a lifter mushrooms at the bottom too much it can get stuck in its cylinder and hold the valve open and pop through the carb. Same pop if the valve goes bad.

Sounds like i got some work to do to it then. better get my other truck running i guess.

[1984Silverado4x4]

well it wont even idle now. it just backfires and dies. I think when i get my other truck back from the shop ill just rebuild this ones engine.

I was told that by the guy i work for it should be 14 something and i was sure he said pounds but maybe he did say Hg.

[xtreme80]

This really sounds ignition related.

Try unplugging the vac. advance on the distributor and plugging the carb (so no vac. leak) and run it then.

Also sounds like it could be a bad pickup coil in the dizzy...

[1975stepside]

Yeah, jeeze, don't go rebuilding it because of this problem! If all else fails you can actually (shudder at the thought!) take it to a mechanic, right? Anyhow, you might want to check your vacuum lines, a vacuum leak can make it run funky and pop and sputter. I prefer to use WD 40 instead of carb cleaner (MUCH less chance of an engine fire that way) and spray around your vacuum lines while it's running. If it smooths out when you spray it, then there's a vacuum leak. Replace the hose for a buck or two and you're good to go!

[1984Silverado4x4]

[QUOTE=1975stepside;2378202]Yeah, jeeze, don't go rebuilding it because of this problem! If all else fails you can actually (shudder at the thought!) take it to a mechanic, right? QUOTE]


I cant afford to take it to a mechanic. If they fix this something else will break. Besides i like the look of a clean painted engine with shiny chrome.

[f.monroe]

I find it best to stop at a point and start over . How was it running before you changed the plugs and wires ? If it was good and you were just doing a tuneup , something didnt get put back correctly or they sold you the wrong plugs . What plugs did you install and at what gap . It sounds like the plug wires are off one terminal and the timing is way retarded . If a previous owner pulled the distributor and didnt get it back in correctly , they may have jumped the wires around the cap to compensate . Did you make sure where the number one wire was connected on the cap before removal ? Main thing is how did it run before ? Frank

[pkbinplano]

almost sounds like a cracked cap

[1984Silverado4x4]

Originally Posted by f.monroe

I find it best to stop at a point and start over . How was it running before you changed the plugs and wires ? If it was good and you were just doing a tuneup , something didnt get put back correctly or they sold you the wrong plugs . What plugs did you install and at what gap . It sounds like the plug wires are off one terminal and the timing is way retarded . If a previous owner pulled the distributor and didnt get it back in correctly , they may have jumped the wires around the cap to compensate . Did you make sure where the number one wire was connected on the cap before removal ? Main thing is how did it run before ? Frank

It idled and ran good before but it was only running on 5 or 6cyl maybe. I put all the wires back in the same place none of them are backwards or connected wrong. There AC Delco plugs and i think there .40 or something like that. Ill have to check to make sure

[piecesparts]

Troubleshoot first, THEN rebuild if all else fails. It will make you mad to rebuild and find out later that there was a simple answer to the problem. The coughing and sputtering problem--Did it start AFTER your change out of the plug wires and ignition parts? If so, then go back to what you know has changed. The coil could be not grounding properly, the plug wire might not be right, even if you checked them--have someone back you up on that--it is easy to get skunked by something that you have been looking at to long.

The ignition module (inside the distributor) is another source of pain in these trucks. Get a new one--it is cheaper than a rebuild and if it is not the proble you are still better off. Be sure to use "Dielectric grease" when you put the module i n, so that it does not go to ground. If you have already changed out the module---did you use the grease---if not put some in>

That intake vacuum reading is in inches not pounds and 12" to 14" is a normal expected reading, look at this. Do a compression check on the engine and see if the valves are bad or not. The carbs are prone to having accelerator pump problems --rough acceleration issues and also wear problems inside the body that cause poor transition from the primaries to the secondaries (rough/harsh cutting out when you accelerate hard).

Do you know if the truck has experienced a failure of the timing chain in the recent past? GM has a problem in this area and if it fails there are things that will happen due to that. Bent valve pushrods or bent valves is common and if so they may need to be repaired through head work. This will give a poor performance issue and rough engine operation

[1984Silverado4x4]

Originally Posted by piecesparts

Troubleshoot first, THEN rebuild if all else fails.

All else has failed it ran for about 2 seconds today then coughed and died and never started again so i didnt get to work today.

It needs a rebuild anyway and i was planning on doing it some time during my ownership.